Methods and systems for compressing and transmitting media signals are known in the art. Compressed digital video is largely becoming the preferred medium to transmit to video viewers everywhere. Parts of the Moving Pictures Experts Group (MPEG) specifications are standardized methods for compressing and transmitting video. The Telecommunication Standardization Sector of the International Telecommunication Union (ITU-T) also defines various compression standards including H.261, H.263, H.264 and the like.
In general, MPEG as well as ITU-T standards are used today for transmitting video over terrestrial, wireless, satellite and cable communication channels and also for storing digital video.
Some standardized compression/encoding standards utilize various compression schemes, such as adaptive quantization, intra-frame encoding, inter-frame encoding, run length encoding and variable length coding. Intra-frame coding takes advantage of spatial redundancies in a picture. Inter-frame coding takes advantage of temporal redundancies from picture to picture in a video sequence. Inter-frame coding involves motion estimation and motion compensation. Motion estimation involves searching, for each block (including N×M pixels, whereas N usually equals M), within a predefined area, a best matching block. The relative positions of these blocks are referred to as motion vector. Motion compensation involves calculating the differences between each block and the best matching block and encoding said difference by a spatial transformation, such as a Discrete Cosine Transform (DCT).
The block-based encoding has resulted in blocking artifacts. These artifacts appear at the boundary of adjacent blocks. This problem is usually more acute in low bit rate transmission systems, in which substantially strong quantization operation is applied.
In order to overcome these blocking artifacts two type of deblocking filters were introduced. The first type is known as a post filter and the second type is known as a loop filter (or in-loop filter). The first type is applied after the encoding process ends while the loop filter is applied as a part of an encoding scheme. Encoders that include loop filter are characterized by better image quality.
Deblocking filters of the first and second types are described at U.S. patent application 20040076237 of Kadono et al., titled “Coding distortion removal method, moving picture coding method, moving picture decoding method, and apparatus for realizing the same, program”, which is incorporated herein by reference.
U.S. patent application 20010020906 of Andrews at al., titled “deblocking filter for encoder/decoder arrangement and method for divergence reduction”, which is incorporated herein by reference, describes a loop filter.
“Adaptive Deblocking Filter”, by P. List, A. Joch, J. Lainema, G. Bjontegaard and M. Karczewicz, IEEE transactions on circuits and systems for video technology, Vol. 13, No. 7, July 2003, which incorporated herein by reference, describes a H.264/MPEG-4 compliant adaptive deblocking filter.
A typical deblocking filter, and especially an H.264/MPEG-4 compliant deblocking filter can apply different filtering operation (in other words—operate in various filtering modes) in response to a boundary strength parameter. The different filtering modes differ by the strength of deblocking filtering applied to the image data.
The deblocking filtering is very complex and requires many computational resources. Typically, a processor that executes dedicated software implements the deblocking filtering process. This approach has two main disadvantages—the processor is relatively power consuming and is also occupied with many tasks that are halted during the whole encoding process.
There is a need to provide an efficient system and method for performing deblocking filtering, especially in cellular phones.